The present invention relates, in general, to an improved titanium-sapphire (Ti:S) pumped optical parametric oscillator, and more particularly to a high power, high repetition rate, intracavity-doubled optical parametric oscillator capable of producing femtosecond pulses tunable in the visible range.
Since the first demonstration of a high-repetition-rate femtosecond optical parametric oscillator (OPO), which was pumped intracavity by a colliding-pulse mode-locked dye laser there has been considerable interest in the further development of such devices. See, for example, D.C. Edelstein et al, Applied Physics Letters 54, page 1728 (1989); E.S. Wachman et al, Optics Letters 15, page 136 (1990); and E.S. Wachman et al, Journal of Applied Physics 70, page 1893 (1991). As a result of this interest, laser pulses in the femtosecond (fs) time domain have become important tools for studying extremely short duration events such as chemical reactions, for by directing femtosecond pulses at reacting chemicals, for example, researchers can capture spectroscopic information about the structure and behavior of short-lived molecular intermediates of the reactions. Femtosecond lasers, which have pulse widths of from 10.sup.-15 to 10.sup.-13 seconds, are also important for studying the dynamics and ultimate limits of high-speed semiconductor electronic and optical devices.
As pointed out in co-pending application Ser. No. 07/880,656 of Pelouch et al, filed May 11, 1992 and assigned to the assignee of the present application, a lack of suitable laser pump sources initially hampered the development of devices capable of operating with short pulses, high repetition rates and high output power. However, the high peak power at the intracavity focus of a colliding-pulse mode-locked dye laser was exploited to develop the first femtosecond optical parametric oscillator, described in U.S. Pat. No. 5,017,806. This resulted in pulses having widths of about 105 fs, with a pulse repetition rate of about 80 MHz at approximately 3 mW output power. Others resorted to Q-switched and mode-locked lasers to pulse an OPO to produce pulses having a duration of 160 to 260 fs at 4.5 mW average power. The above-mentioned '656 application improved on such devices through the use of an externally pumped, self-mode-locked Ti:S laser for producing high power, high repetition rate femtosecond pulses over a broadly tunable range from about 1.0 .mu.m to about 2.75 .mu.m. The Ti:S OPO of that application offers several desirable operating characteristics such as high output power, extensive tunability, nearly transform-limited pulses as short as 57 fs, excellent stability and low amplitude noise. However, there is still a need for an improved tunable source of optical pulses that can operate with a high average output power, short pulse widths, and which is tunable over a range of wavelengths to produce output light which has a shorter wavelength than such prior devices.